High resolution exposure devices may be used in the manufacture of highly integrated semiconductor devices. Some high resolution exposure devices use a deep-ultraviolet (DUV) light source of 248 nm wavelength to expose a 250 nm pattern. Some other exposure devices use a DUV light source of 193 nm wavelength to expose a 100 to 130 nm pattern. Recent advances in exposure devices have enabled the use of an extreme ultraviolet (EUV) source, a so-called soft X-ray radiation source, to obtain an exposure pattern with a size that is less than 100 nm, and which may be capable of obtaining pattern sizes from 5 to 70 nm.
Exposure devices that use EUV differ from those that use DUV because, for example, most materials have high light absorption in EUV regions, leading to the use of a reflection photomask instead of a transmission photomask. An EUV photomask may include an absorber pattern that is formed on a reflector (mirror). The absorber pattern is highly absorptive to EUV radiation, and the reflector has a high reflectivity to EUV radiation.
FIG. 1 is a cross-sectional view of a conventional reflection photomask 100. A multi-layered reflection layer 20 is formed on a substrate 10 of silicon or glass. A soft X-ray absorber pattern 30 made of tantalum nitride TaN and having a predetermined pattern is formed on the reflection layer 20.
When the absorber pattern 30 is patterned, the reflection layer 20 may become damaged and its reflectivity may be decreased. The reflection layer 20 may become polluted, or contaminated, when the reflection photomask 100 is used during an EUV exposure process. Pollution of the reflection layer 20 may include oxidation from the decomposition of H2O and/or hydrocarbon in the presence of high EUV light and/or by the deposition of carbon on the reflection layer 20. Pollution of the reflection layer 20 may decrease the reflectivity of the reflection layer 20.